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MOT Tesla Coil help

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Munkey

Thu Feb 28 2008, 10:12PM

Registered Member #588 Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93

Ive been wanting to build a SGTC (or any good) Tesla Coil for some time, since I can't get my hands on a NST I was left with using MOTs. But how do I go abouts this? Thats a bit of a general question but what I want more specifically is the calculations to for the values of the components I am going to use, and any other possible aspects I have overlooked.

I did have a program which I can't find any more called Wintesla- that did the calculations for me, but that was useful only for a NST.
I have looked on the deepfriedneon.com site and using their calcualtors I have found out the correct tank capacitor size to match my tranny, so how do I enter this into the rest of the components? primary/secondary coils, topload and spark gap distance...

Thanks for any help.

MOT_man

Fri Feb 29 2008, 03:37AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

Well from experience I can say that MOT powered coils produce stiff currents and use fairly decent sized capacitors. A friend of mine ran a quad pack MOT supply off a 240V 30A socket - secondary output was 9.6 kV AC @ 600 mA - primary capacitance was 0.12 uF @ 35 kV DC.

MOT power supplies need secondary side MO caps as ballasting loads - 1 uF 2.5 kV AC rating X 2 in series on each side will allow serious current to flow in the system.

Munkey

Fri Feb 29 2008, 06:43PM

Registered Member #588 Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93

Ok, I will be using only one MOT so is ballasting still necessary?

So how do I find out the values of the primary and secondary coils?

Also, do you know how well a load MOT caps in series will serve as the tank capacitor...

SilentPhoenix

Fri Feb 29 2008, 06:53PM

Registered Member #1258 Joined: Wed Jan 23 2008, 11:52AM
Location: Haarlem, Netherlands
Posts: 20

if you read this

thoroughly and use these

equations and formulas you should be able to calculate everything, from the secondary diameter/height ratio to the length of wire needed to make it.
this

site also offers a load of info on the subject and some usefull calculators.
i have a few NST's lying around but i don't know if it's possible to ship them to the uk since they're quite heavy... have you tried writing/calling a local neon shop?

Munkey

Fri Feb 29 2008, 08:43PM

Registered Member #588 Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93

Yes, I have looked through the calculator pages on deepfriedneon and theres nothing that I can see that 'connects' the tank capacitor + transformer to the primary /secondary. Its just to find out the values of your coil.

So I have a transformer and a capacitor to match, how do I find the value of the primary coil?

I have looked in dumpsters for NSTs but no luck. I have done some looking and there is no neon sign shops nearby that I can raid.

Edit: Whats the average current a MOT can output? I assume the voltage is about 2.5kV...

Myke

Fri Feb 29 2008, 10:56PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

Current is about 500mA @ 2KV for most MOTs. That what it seems like.

MOT_man

Sat Mar 01 2008, 02:33AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

I have several large core MOTs - 1100 watt oven types. Will an Ammeter attached to the secondary side these transformers can pull 800 -1000 mA under a short condition. Average voltage output is 2200 V.

MOT capacitors are NOT suitable for a rapid pulse discharge capacitor. They will either burn up or EXPLODE violently. -- I know this from experience too.

CDE 942C series of capacitors are excellent for Tesla Coil usage - I use the 0.68 uF 1600VDC rated caps in my tesla coil. WOW!! These capacitors are fantastic at $4.30 per capacitor.

teravolt

Sat Mar 01 2008, 06:36AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I just bought 2 1200va MOTs + S/H for 38$ on ebay. if the two MOTs are out of phase you can get 4400vac between the outputs. this done by reversing the input on one transformer from the other. if you want to dubble current put them back in phase and connect the outputs together. the cde 94220p15kf caps are 2.87$ in quantities of 50 are availible at richardson electronics. for a mot tesla they can be seriesd or you can get them with a 3000vdc rating. when you by caps remember that the peak voltage of a mot rms voltage is 1.14 *Vrms or 1.14*2200=2508Vp. your cap DC voltage rating should be about 40% grater than this. happy hunting N.B.

Munkey

Sat Mar 01 2008, 08:11AM

Registered Member #588 Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93

I doubt I would use 2 MOTs- Too much power and more things to go wrong. I was also going to try out using 2 MO caps in series as the tank capacitor, just to see if it would work. Lucky you said not.

I am going to have a look around for some cheap caps, I may end up making my own from something...

So lets assume I have the correct value capacitor with the transformer. How do I find out the inductance of the primary coil?

vasil

Sat Mar 01 2008, 06:59PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

You can try inductive ballast on the primary side of your MOTs. I used ballast coils (drossel) from high pressure Hg lamps rated at 250 watts.
The project is HERE

Upgrading the primary cap to 35 nF and using multiple spark gap, the results are just nice:

MOVIE

Good luck!

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